That’s just the general rule of thumb starting point. Obviously there are other factors going on here, and that will affect how the balance is determined. For instance, can the scum use stones they’ve stolen? If so, they could become much more powerful, and tip the scales heavily in the process.
Also, I will note that the OP states any stones Thanos has when he dies are removed from the game. This implies the game will not end with his death, and there is some other group of people to be on the lookout for, whether they are aligned with him or not.